Heat sensitive copy sheet, process of making and using



June 18, 1963 w. R. woRKMAN 3,094,417

HEAT SENSITIVE COPY SHEET, PROCESS 0F MAKING AND USING Filed Jan. 3. 1961 Pape//ke back/hg.

VII'IIIIII IIIIIIIIIIIIIII IHHQEHHEIIBEHHEIB Illlllllllllllll United States Patent O 3,094,417 HEAT SENSITIVE COPY SHEET, PROCESS F MAKING AND USING Wesley R. Workman, St. Paul, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Filed Jan. 3, 1961, Ser. No. 80,184 25 Claims. (Cl. 96-28) This invention relates to heat-sensitive copy-sheets and methods of making and using the same, and has particular reference to the formation of high quality heatstable reproductions of both black-and-white and colored graphic originals.

The practice of thermographic reproduction, as previously described, involves briey exposing a ditferentially radiation-absorptive graphic original to intense radiant energy while in contact with a heat-sensitive copy-paper. Typically, the copy-paper comprises a normally stable visibly heat-sensitive layer of chemically inter-reactive components which react together to form a visibly distinct reaction product when the copy-sheet is heated momentarily to a conversion temperature within the approximate range of 90 to 150 C. The heat-pattern established at the irradiated original causes a corresponding visible pattern to appear in the heat-sensitive layer, without deterioration of the original. The unheated areas of the copy-sheet remain heat-sensitive and unchanged.

Tungsten iilament lamps provide a convenient and greatly preferred source of radiation for thermographic reproduction. The radiation provided is rich in infrared as Well as visible light, and the process is therefore particularly suited to the copying of originals having infra-red-absorptive image areas. Penciled notes and sketches, type-Written correspondence, and printed books or documents having black infra-red-absorptive markings on reflective or transparent paper or film backgrounds are copied with particular effectiveness.

The present invention makes possible the reproduction, on heat-sensitive copy-paper, of graphic originals having variously colored as well as black image areas.

Permanent copies are provided, in which the background areas are no longer heat-sensitive. Image resolution is improved, particularly in the copying of originals having both very small and very large inked image areas; half-tones, for example, are faithfully reproduced without blurring or loss of detail. As with the earlier heatsensitive copy-sheets, the products of this invention require no treatment with chemical fumes, vapors or solutions, soivents, dusts or powders, in providing visible reproductions of the graphic originals. Instead, copies are produced by simple irradiation and heating such as may readily be accomplished with tungsten filament lamp systems, the radiation being largely in the higher visible and infra-red region.

Many visibly inter-reactive chemical systems have heretofore `been described, and others are constantly being devised, which are useful in thermographic heat-sensitive copy-sheet structures. The reactants are preferably maintained in physically distinct and chemically interreactive relationship as intimately dispersed reactant particles in a suitable hlm-forming binder, applied as a thin coating on a paper or paper-like backing member. Many such copy-sheets, although fully reactive when momentarily heated to conversion temperature, are completely indiierent to visible light, and remain unchanged even after prolonged exposure. Others are stable towards visible light of higher wavelength but gradually change in heat-reactivity when exposed for prolonged periods to radiation in the near ultra-violet.

The present invention provides th-ermographic copy- ICC sheets which, while normally fully capable of undergoing visible change on brief heating at conversion temperatures in the approximately to 150 C. range, may be made insensitive to such heating by moderate irradiation with visible light, particularly in the green, red and yellow regions.

A wide variety of compositions has been found useful in the practice of the invention, such that no definitive chemical classification of required reactants has been found possible. However the reactants and reactant systems may be adequately defined by means of certain tests. In all cases the two or more essential reactants undergo permanent visible reaction when the sheet is momentarily heated to the conversion temperature in the thermographic copying process. In addi-tion, the reactants undergo the same color-forming reaction when mixed together in solution in a suitable solvent, with gentle heating if necessary; whereas the reaction is prevented when one or another of the reactants, in solution, is first exposed 'to radiation at wavelengths in the nearultraviolet region of about 3000 to about 4200 angstroms.

The test is conveniently nun as follows. Given a visibly heat-sensitive system consisting essentially of two inter-reactant materials A and B, material A is first dissolved in an inert liquid solvent at low concentration. The solvent is selected to be non-reactive with either of fthe reactant materials, and neither absorbs nor is altered by the actinic radiation employed. The concentration of material A is just suiicient to produce a distinctly visible reaction with material B. A portion of the solution, in a small transparent quartz test tube, is exposed to radiation from a BH-6 high pressure mercury arc lamp at 6 inches from the sample for a time up to 45 minutes. A second portion is retained as a control. A small amount of material B s then mixed into each of the irradiated and the non-irradiated portions, with heating on a water bath to about 60 C. where required, and the two solutions are compared for color. A system in 1which the color of the test solution is widely different or decidedly reduced in intensity from that of the control solution is, by definition, a readily desensitizable system as that term is here employed, and is useful in the practice of the invention.

Certain typical reactants, in particular 4-methoxy-lnaphthol as employe din system l and in Examples l and 3 appearing hereinafter were additionally tested under more restrictive conditions. Radiation from the BH-6 lamp was first passed :through a Corning CS 0-54 filter before reaching the test solution. After 5 minutes the solution was removed and a small amount of silver behenate (reactant B) was added. The irradiated portion remained a light yellowish color; the control sample turned an intense blue. Another sample was irradiated through a Corning CS 3-72 filter, in this instance for 45 minutes; both the irradiated and the control portions produced the blue color on addition of silver behenate. The 0-54 color standard transmits radiation of wavelength above abont 3000 angstroms; the 3-72, above about 4200 angstroms, i.e. in the visible range. Green, yellow and red radiations lie in the upper visible wavelength range of about 4500 angstroms to about 7000 angstroms. It will be seen that these radiations had no observable effect on the reagent under test.

In some instances it may be found more convenient to make the color comparison' by first saturating a piece of white filter paper with a solution of reactant material B, drying the paper, placing a drop of the solution of reactant material A on the treated area, and brielly heating the paper to conversion temperature. Placing a drop of the irradiated test solution and a drop of the protected control solution on the treated paper in side-by-side position makes possible a quick and effective comparison.

Some typical examples of readily desensitizable visibly heat-sensitive systems and of a few heat-sensitive systems which cannot be desensitized, as determined by the above test, follow. In each instance the solvent employed is methanol, and the radiation is in the near-ultraviolet range of approximately 3000 to 42000 angstrorns Wavelength. The molar concentration is stated for each reactant material A except where otherwise indicated. The time of irradiation is given in minutes, and the difference in color between control sample and test sample is indicated. The designation no change indicates that the reactivity is not influenced by the irradiation.

Time Irmdiated Reaetants Conc.

Untreated A 4 -methoxy-l-naph- B hsilver behenate A dithiooxamlde B nickel stearato dihyd ropyrogalloL B silver behenate. ascorbyl palmitate B silver behenate A l-phenyldithiohydrazoearbonamide.

yellow.

colorless.

yellow.

gray.

yellow.

yellow.

brown.

colorless.

gray.

10. colorless.

no change no change no change gallic aci Nnitrosodiphenyl amine.

It will be appreciated that many other systems and other specific reactants may be added to, or substituted in, the foregoing tabulation. As one example, reactant A of system 1 may be replaced by such materials as 2-methyl-4-rnethoxy-1-naphthoL 4 ethoxy 1 naphthol, 4,4'-dirnethoxy1,l'-dihydroxy-Z,2'binaphthyl, 1,4 dihydroxynaphthalene, 1,3 dihydroxynaphthalene, 1,5 dihydroxynaphthalene, the condensation product of 1,5-dihydroxynaphthalene with acetone or with adipoyl chloride, or other cyclic organic reducing agent for silver ions, having an active hydrogen atom attached to a nitrogen, oxygen or carbon atom which is directly attached to an' atom of the cyclic ring and which is also readily desensitizable. Likewise, the silver behenate reactant B of system l may be replaced by other normally solid organic acid salts of noble metals. Mixtures of reactants A or reactants B may also be used in this and other systems.

Again, reactant A of system 2 may be replaced with substituted dithiooxamides such as N,N'didodecyldithio oxamide, N,N'-diphenylethyldithiooxamide, N,Nbis(o chlorobenzyl) dithiooxamide, N,N' bis(carboxyamyl) dithiooxamide, N,N' bis(2 (N" ethyl m toluidino) ethyl)dithiooxamide, N,N'-dibenzyldithiooxamide, and N,N'-difurfuryldithiooxamide; the last-named compound being particularly useful. The nickel stearate reactant B ot system 2 may be replaced with nickel benzoate or with equivalent heavy metal salts, for example of cobalt or copper.

Reactant system 8 as hereinabove defined seemingly is an exception in that the color change becomes apparent mainly on cooling the heated dry mixture from the conversion temperature. Since only momentary heating is employed, and the system is therefore returned at once to room temperature, this difference is not regarded as significant, the practical results in terms of colored image areas being unchanged. However the difference must be taken into account in testing to determine whether or not such reactant materials are readily desensitzable.

Reactant systems including a a readily desensitizable component may be incorporated into heat-sensitive copy sheet structures in a variety of ways. The reactants may be intermixed, together with suitable binders, plastieizers, fillers, and other additives `and modifiers as desired, and applied in a single thin coating to paper or ilm backings. The procedure is economical, since only a single coating and drying step is needed. The reactants may be separately dissolved or dispersed in appropriate binder solutions `and applied to a common backing sheet in two separate contiguous layers, with or without a permeable or temporary separating barrier layer. Two or more separate coating steps, with intermediate drying, are required; and since reaction occurs mainly at an interface, some decrease in image density is frequently observed. However the two reactant materials have no opportunity of pre-reacting in solution', and a wider choice of binders and solvents is made available; the procedure is therefore particularly useful in the preliminary testing of reactant systems. The two solutions or suspensions may also be separately applied to separate backings to form cooperating intermediate and receptor sheets which when later placed in face-to-face relationship form the heat-sensitive copy-sheet product, the image-forming reaction again occurring at the interface.

Surprisingly, it has now been found that the incorporation of small amounts of certain activatible silver-reducing organic dyes in intimate admixture with the radiationsusceptible components of readily desensitizable rapidly heat-reactive systems as hereinbefore defined makes possible the construction tof heat-sensitive copy-sheet materials which are permanently visibly changed on brief heating in the thermographic reproduction process or by momentary contact with a metal test bar at conversion temperature, and which are desensitized by moderate exposure to visible light at wavelengths about 4200 angstroms, and, more signicantly, at the higher wavelengths above about 4500 angstroms and including green, yellow and red radiations. As a result, copy-sheet materials are now made available with which heat-resistant permanent copies of originals printed in colors as well as blackand-white may be prepared `on thermographic heat-sensitive copy-sheets by irradiation alone; images of specific color may be selectively copied by employing sources which selectively emit light of the designated wavelength, and, conversely, copy-sheets may be designed for selective operati-on with specic light-sources or with originals printed in specific colors; both tine lines and heavy blocky areas of graphic originals may be simultaneously copied with excellent image resolution on heat-sensitive copysheets; and `other advantages in terms `of both process and product may be obtained.

As with the radiation-susceptible reactant compo-nent, it has been found impossible, in the present state of knowledge, to offer a definitive chemical classification of dyestuffs operable for the purposes of this invention. The problem is made more difcult by the wide complexity of the visibly inter-reactive compositions themselves. However, it has again bee-n found possible to distinguish the operable dyes by means of a simple chemical test performed in solution and involving the reduction of silver ion to metal, the procedure for which will now be described.

A solution is prepared, in an inert neutral light-stable liquid solvent, containing, per liter of solution, approximately .001 mole of silver nitrate, .0l mole of triethanolammonium nitrate (prepared, for example, by neutralizing triethanolarnine with nitric acid), and .0001 mole of the dye. The concentrations are not critical but should be of the indicated order of magnitude. Water is a preferred solvent where the dye to be tested is soluble therein; methanol, dioxane, or mixtures of these with water are useful with dyes which are insoluble or partially soluble in water alone. Two -rnl. portions are placed in Pyrex test tubes in a water-bath at 50 C. One is protected from light; the other is irradiated for 30 minutes with light from a 500 watt tungsten filament projection bulb at a distance of 8 inches from the sample, i.e. at an intensity of about 60,000 foot-candles. The two tubes are then visually compared. The control tube is found to contain a visible trace of precipitated silver, ordinarily as a fine black powder. In the presence of an activatible dye, the amount of silver precipitated from the test solution is significantly increased. Large increases may be estimated visually; or the amounts of precipitate may be determined by quantitative analysis. Precipitation of silver under test conditions may occur in the form either of dense black liakes or of a silver mirror on the clean Wall of the tube. Although not ordinarily required, the silver precipitate may be distinguished from precipitated portions of dye or other materials by its insolub-ility in excess of organic solvent.

Copious precipitation of silver occurs in the just-described test when applied to halogen-containing fluorescein dyes, for example erythrosin, Rose Bengale, D & C Orange #16, and Aizen Acid Phloxine PB, and to para rosaniline dyes, for example Calcozine Violet Ex. Conc.; and these dyes are also found to produce rapid loss of heat-sensitivity when incorporated in heat-sensitive copysheets using, for example, the reactant components of system 1. Additional examples of dyes which have been found to be less effective, but still useful for the purposes lof the invention, include Eosin OI Purified, Rhodamine B Extra S, Pontacyl Violet S4B, Pontachrorne Azure Blue B, Phenosafranine, Fast Pat Blue B, Artisil Orange SRP, Tin-on Yellow GK-F, Calcozine Blue ZF (methylene blue), Aizen New Methylene Blue NHX, Seto `Flavine T, proflavine hydrochloride, Azo Scarlet Y, and Kryptocyanine. Mixtures of dyes may be used. In each instance the dye is a colored organic compound which absorbs light in the visible wavelength range above about 4200 angstroms, which causes reduction of silver ion and precipitation of metallic silver under the test con ditions hereinbefore described, and which both renders the resulting copy-sheet desensitizable under irradiation with visible light, and also provides a significant increase in ithe rate of desensitization.

The following examples illustrate but do not limit the invention.

Example 1 Map overlay tracing paper is coated with a suspension of 10 parts by weight of silver behenate in a solution of 1 pant of phthalazinone and 3 parts of Parapol S50" styrene-isobutylene copolymer in 86 parts of heptane. The mixture is prepared by extensive milling in a ball mill and is applied by means of a coating bar set at an orifice of 3 mils. The coating is dried. A further coating is then applied, at an orifice of 2 mils, of a solution of .042 part of 4methoxy1naphthol, 1.005 parts of ethyl cellulose, and .00435 part of prolavine hydrochloride in 9.03 parts of methanol. The coating is applied and dried under subdued light and at normal room temperature. The sheet has a light yellow color.

A graphic original, in this case printed Vin black ink on thin white paper, is placed with the unprinted surface in contact with fthe copy-sheet thus prepared, and the composite is brielly intensely irradiated as in the thermographic back-printing procedures. A blue-black reproduction of the original printed image is produced on the copy-sheet. The copy is then irradiated for 45 seconds at 20,000 foot-candles with light from a 300-Watt incandescent-lament projection lamp. No visible change occurs in the copy-sheet, and the background areas are found to be stabilized against subsequent visible change on heating. Similar stabilization occurs, more slowly, under exposure to ordinary room light, e.g. from incandescent lamps or indirect sunlight.

The phthalazinone is not essential to the reaction but aids in producing an attractive appearing image.

A further graphic original, prepared by writing on thin semiaransparent paper with each of red, yellow, green and lblack infrared-transrn=issive inks, is placed over a fresh section of fthe copy-sheet and the printed surface is irradiated with light from the same source, again lior 45 seconds at 20,000 foot-candles. The copy-sheet is then heated briefly by exposure to air at C. in an oven for a few seconds. A blue-black copy of the inked image areas is obtained. The image outline is par-tcularly sharp.

A control sheet prepared in exactly the same manner except for the omission of the prollavine hydrochloride is equally sensitive to heat but is not heat-stabilized by the radiation treatment although continued for many times the exposure given the dye-containing sheet.

Pigments such as zinc oxide, fillers such as powdered silica, resins such as powdered high-melting terpene resins, toning agents other than phthalazinone, and various other modiliers and additives may be included where desired. They may be incorporated in either layer or in an appropriate intermediate or outer layer, but preferably in the first or sub coat along with the silver behenate and resinous binder.

The ethyl cellulose polymeric film-forming binder of the second coat is applied in solution in a non-solvent for the styrene-isobutylene copolymer binder of the tirst oeat, thus avoiding intermixing and possible inter-reaction .at the interface during coating and drying. The presence of the silver behenate as dispersed particles also is of assistance in maintaining the reactants in physically distinct but chemically inter-reactive relationship. Various other binder materials may be substituted for either or both of the polymers here employed, with equally good results where proper precautions are observed as to solubility, compatibility, softening temperature and other properties as indicated by the illustrative embodiments here described. For example, a sheet prepared essentially as herein indicated, but in which a polyvinyl acetate resin binder is used for the silver behenate first coat composition, is found to be equally useful when the ethyl cellulose binder for the dye-containing methoxynaphthol second coat composition is replaced by chlorinated rubber, polyvinyl acetate, polyvinyl butyral, cellulose acetatebutyrate, polystyrene, polyvinyl pyrrolidone, or Vinylite VMCH a copolymer of vinyl chloride, vinyl acetate and maleic anhydride. In each instance the composition contains two parts by weight of erythrosin to 15 parts of methoxynaphthol and 1100 parts of binder. ln each in-V stance the sheet material as initially prepared forms black image areas when briey held in Contact with a metal test bar at C. In each instance the sheet is prevented from thus darkening by irradiation for l2 minutes with light from a BH-6 lamp through a 3-72 lter. In the absence of the dye component, the sheet is prevented Lfrom heat-darkening when similarly irradiated through the 0-54 filter, but remains fully heat-sensitive when irradiated through the 3-72 filter, i.e. with visible light.

Example 2 Map overlay tracing paper is coated with a thin anticurl layer of Lucile 44 tertiarybutyl methacrylate polymer and is then further provided with a coating, at an orilice of 3 mils, of a ball milled mixture of 5 parts by weight of ferrie stearato, l part of l-phenyl-dithiohydrazodicarbonamide, 2.5 parts of ethyl cellulose, .07 part of erythrosin and '66 parts of methanol. After being dried at room temperature and under subdued light the sheet is light red in color and is heat-sensitive, producing black image areas when locally brielly heated as in the thermographic copying process. The background areas are then made heat-insensitive by irradiation with white light.

Background areas of the copy-sheet may lirst be rendered insensitive to heat by irradiation for one to two minutes with white light at an intensity of 32,000 footcandles through a photographic transparency, after which the sheet is heated to provide black image areas on a contrasting background. In the absence of the erythrosin, the coating remains visibly heat-sensitive after exposure for 30 minutes under the same conditions.

The lluid composition may be coated on a temporary carrier, dried, and removed in self-sustaining tilm `form by stripping, to provide an exceptionally thin heat-sensitive copy-sheet. Other backings may be used. The exposed sensitive layer `may be further provided with a thin transparent protective surface film or coating if desired, for example of ethyl cellulose or polymethyl methacrylate.

Example 3 Thin transparent Mylar polyester film is coated at 3 mils with a solution of .2 part by weight of 4-methoxy-lnaphthol, .088 part of erythrosin and l parts of ethyl cellulose in 90 parts of methyl ethyl ketone, and dried in total darkness, producing a reddish light-transmissive sensitized intermediate film member.

White paper is coated with a continuous thin colorless layer of a ball milled mixture of parts of silver behenate, 1 part of phthalazinone, 3 parts of poly-t-butylmethacrylate and 86 parts of acetone, and dried, producing a white receptor sheet.

The colored film is first placed with its coated surface in contact with a multi-colored original having image areas printed in black, red, green and blue inks on heavy White paper and the composite is irradiated from the film side for 14 seconds with light from a 500-watt tungsten filament projection lamp at 16 inches distance, i.e. at an intensity of about 10,000 foot candles. The thus exposed film is then placed with its coated surface in contact with the coated surface of the paper receptor sheet and the composite is pressed between flat glass panels, previously heated to 110 C., for a few seconds. Alternatively the composite may be passed around a heated bar or between squeeze rolls of which one or both is maintained at the required elevated temperature. An intense blue-black and very sharp image is formed on the paper sheet, corresponding to the inked image of the original, and is clearly visible through the colored iilm, `which however is preferably removed and discarded.

In the absence of the erythrosin, the procedure described fails to produce a copy on the coated paper receptor sheet, the entire coated surface becoming uniformly blackened.

Substitution for the coated paper receptor sheet of a sheet of Mylar" polyester film coated with a solution of ethyl cellulose binder and chlorobenzenediazonium hexailuorophosphate provides an intense red image on the receptor lm when heated at 110 C. for 30 seconds in pressure-contact with the irradiated colored sensitized intermediate film.

A different receptor sheet useful in conjunction with the sensitized red intermediate iilm in the process of the example is prepared by coating paper with a mixture of silver behenate, phthalazinone, and 4-benzoylamino2,5 diethoxybenzenediazonium chloride, together with poly-tbutylmethacrylate binder resin. Image areas formed by heating the imaged film in contact with the receptor sheet are blue in color and are highly absorptive of infra-red, making possible the preparation of further copies by conventional thermographic copying procedures on heat-sensitive copy-papers.

Another receptor sheet useful in connection with `the intermediate film member of the example employs Nap-hthanil Diazo Blue G active diazonium salt coated on white paper, in this instance with no added film-forming binder. Another employs Lusane Brilliant Blue B copper phthalocyanine precursor.

Receptor sheets containing silver behenate or other noble metal soaps are similarly useful in conjunction with lightdesensitizable intermediate film products in which 2,5-diaminotoluene replaces the methoxynaphthol component of `Example 3. A typical formulation contains .06 part of 2,5-diaminotoluene, .024 part of erythrosin, 3 parts of ethyl cellulose and 27 parts of methanol. The dried coating darkens a silver behenate recep tor, when heated in contact therewith, only if not previously exposed to visible light. In the absence of the dye component, exposure to visible light has no desensitizing effect,

Further examples of light-desensitizable, heat-sensitive compositions and copy-sheets which have been shown to be useful in the practice of the invention will now be presented in abbreviated form. For convenience, the inter-reactive components are separately dissolved or dispersed and are applied in two layers, as more fully described in connection with Example 1, the dye being incorporated with the readily desensitizable component. With appropriate modification, particularly as to solvent and binder components and with proper proportioning of the two mixtures, these systems may be applied as single-layer coatings, eg. as described under Example 2. Where one or another of the reactants is volatile at conversion temperatures and is readily transferable, e.g. as is the rnethoxynaphthol component in the structure and procedure shown in Example 3, the system may be supplied `and used in the form of separate but cooperative sheet or iilm laminae as there illustrated. The resulting heat-sensitive copy-sheets are rapidly desensitized on exposure to visible light at wavelengths above about 4200 angstroms, or more particularly at wavelengths above about 4500 angstroms.

Proportions `are given in parts by weight in these examples. Since reaction occurs largely at the interface between the two coatings, the relative thicknesses and unit weights of the two are of no critical significance.

Example 4 First coat: 10 parts of bismuth subnitrate, l part of triethanolamine, 5 parts of styrene-isobutylene copolymer and 35 parts of heptane.

Second coat: .05 part of stannous sulfate, .03 part of triethanolamine, .02 part of Duponol ME sodium lauryl sulfate wetting agent, .005 part of erythrosin, 1 part of water, and 4 parts of methanol.

Example 5 First coat: 5 parts of Naphtol AS-SW" azo coupler compo-nent, 20 parts of polystyrene resin, 40 parts of acetone, and 40 parts of methyl -cyclohexane- Second coat: .012 part of 3,3dimethoxy-4,4'diphen ylene bis (3-methyl3(sodium methylene carboxylate)l triazene), .5 part of polyvinyl alcohol, .8 part of water, 3.7 parts of methanol, and .008 part of erythrosin.

Example 6 First coat: 7 parts of 2-(B-methylbenzthiazolinone) (1'hydroxy2'naphthoyl)hydrazone, l0 parts of styrene-isobutylene copolymer, and 90 parts of heptane.

Second coat: .02 part of N,Nbis(p-toluenesulfonyl)- N,N'-dichloroethylenediamine, l part of polyvinyl alcohol, 1.6 parts of water, 7.4 parts of methanol, and .012 part of erythrosin.

Example 7 `First coat: 1 part of aminodiphenylamine, 2 parts of Naphtol AS-SW, 12.5 parts of titanium dioxide, 20 parts of Vinylite VMCH vinyl resin, and parts of acetone.

Second coat: .04 part of N-nitrosodiphenylamine, .06

9 part of triethanolamine, l part of polyvinyl alcohol, 1.6 parts of water, 7.4 parts of methanol, and .004 part of erythrosin.

Example 8 First coat: 3 parts of nickel stearate, 2 parts of silica powder, 4 parts of polyvinyl acetate resin, and 46 parts of methylethyl ketone.

Second coat: 0.11 part of N,Ndifurfuryl dithiooxamide, .044 part of methylene blue, 5.5 parts of ethyl cellulose, and 50 parts of methanol.

The desensitizable heat-sensitive copy-sheet structures hereinbefore described may be `further modied in numerous ways to provide special effects and for particular purposes, as indicated in the following examples showing a number of typical combinations.

Example 9 Transparent polyester lilm is supplied with la first coating of a mixture of parts of silver behenate, 0.5 part of phthalazinone, .04 part of 4-methoxy-1-naphthol, .004 part of proflavine hydrochloride, and 5.5 parts of ethyl cellulose, applied from methanol. The coating is dried. The sheet is 4heat-sensitive, forming black image areas under thermographic `back-printing procedures, and is rapidly desensitized on exposure to higher wavelength visible light.

There is then applied over the iirst coating a second coating of a mixture of l part of dithiooxamide, 2 parts of silica powder, 3.7 parts of polyvinyltoluene resin binder and 43 parts of heptane solvent, and the coating is dried. Separately a receptor sheet is provided by coat ing a heavy white paper backing with a thin continuous layer of a mixture of 3 parts of nickel stearate, 2 parts of silica powder, and 4 parts of polyvinylacetate in 46 parts of methyl ethyl ketone, which is dried.

The coated lilm is placed with the coated surface in contact with a rdifferentially radiation-absorptive graphic original which is then briefly irradiated through the film with intense infra-red, producing visibly darkened and infra-redabsorptive image areas in the film coating. The film is exposed to visible light, causing desensitization of the undarkened background areas. It is then placed with its coated surface against `the coated surface of the receptor sheet, and again irradiated with infra-red. A dense sharp reproduction of the image areas is produced on the receptor sheet. Several additional high quality copies are prepared on `additional receptor sheets from the same imaged film by successive irradiations.

A somewhat similar eiect is obtained by applying a surface coating of a volatilizable infra-red-transmissive dye, such as Du Pont Oil Blue A, over the surface of the heat-sensitive coating. Formation of visibly distinct and infra-red-absorptive image areas and desensitized background areas in the heat-sensitive coating is accomplished either by application of a heat-image followed by exposure to visible light or by exposure to a lightimage, i.e. through a transparency or stencil, followed by uniform heating. Further irradiation with infra-red of the stabilized imaged copy while holding the dye-coated Surface in contact with untreated white paper serving as a receptor sheet causes localized transfer of dye to the receptor at image areas. Again, several copies may be prepared from a single copy-sheet intermediate.

Less effective but still useful transfer of dithio-oxarnide or dye from imaged copy-sheet to receptor sheet is obtained by incorporating the transferable imaging material directly in the heat-sensitive first coating.

Example I 0 Paper which has been dyed a dark blue is provided with a first coat of a mixture of l0 parts of silver behenate, 1 part of phthalazinone, 6 parts of poly-t-butylmethacrylate and 23 parts of acetone, and dried. A second coat is then applied, consisting of a mixture of .l part of 4 methoxy-lnaphthol, .01 part of erythrosin, 5 parts of ethyl cellulose, 5 parts of water, and 45 parts of methanol. On drying, a porous blushed film is produced which is light pink in color. Exposure to visible light through a transparency or stencil, followed by brief heating at -100" C., produces a faint darkening at the protected image areas. Subsequent brief irradiation with intense infrared causes dramatic further darkening of these areas, the blue paper becoming visible through the thus transparentized blush coating. Further exposure to room light results in gradual fading of the light pink background areas to white, thus still further increasing the contrast between image and background areas.

The same coatings applied to a transparent tilm backing produces a copy-sheet in which the background areas remain opaque and light pink or white in color, while the image areas are essentially transparent. The structure is particularly useful in making projection transparencies.

Example .ZI

Map overlay tracing paper or transparent glassine is first provided with a thin uniform coating of a ball mill dispersion of l() parts of silver behenate, 1.6 parts of phthalazinone, 2.4 parts of Lucite 44 binder, and 86 parts of methylethyl ketone. Over the dried coating is applied a thin uniform coating of a smooth dispersion of 30 parts of titanium dioxide pigment in a solution of 5 parts of ethyl cellulose in 65 parts of acetone, with rapid drying. A further thin uniform coat of a solution containing 10 parts of ethyl cellulose, 0.24 part of 4-methoxyl-naphthol and 0.1 part of erythrosin in 90 parts of acetone is then applied and rapidly dried, e.g. in a current of air at normal room temperature and under subdued light. The copy-sheet product is a deep red color on the coated side but a light pink as viewed through the backing.

The copy-sheet is placed with its coated surface in contact with a printed original having black radiation-absorptive image areas on a white background. Intense white light is rst directed through the copy-sheet and toward the printed surface of the original, to provide complete desensitization at background areas with only partial dcsensitization at image areas. Intense infra-red radiation is then similarly applied, resulting in the formation of clearly visible black image areas on the light pink background of the copy-sheet.

The titanium dioxide imparts suicient vapor-permeability to the ethyl cellulose binder film to allow the methoxynaphthol which is vaporized at the heated image areas to pass through the film and react with the silver behenate.

The titanium dioxide may be incorporated directly in the coating containing the alpha-naphthol and dye, for example by mixing equal amounts of the two mixtures prior to coating, producing a visibly opaque but intensely colored heat-sensitive copy-sheet. A thin surface coating of unpigmented binder is useful in minimizing any dissipation of volatile components from the sheet but tends to interfere with the desensitization of the methoxynaphthol and is ordinarily omitted as in the structure described hereinabove.

The permeable layer may alternatively be replaced by a normally impermeable thin coating of fusible film-forming materials which melts at heated image areas to permit diffusion of the reactant vapor when heated to conversion temperature.

Heat may be applied by conventional thermographic front-printing procedures as described in the example, in which case the heat is concentrated at the image areas. Replacing the printed original with a continuously infrared-absorptive black paper, platen, roller or other surface and irradiating as before causes heating over the entire area, with identical results in terms of the copy produced but without requiring continued alignment of copy-sheet and original. Heat may also be supplied from heated platens or rollers.

Additional structures and applications, a few of which are here briefly mentioned, will be suggested by the foregoing illustrations. The presence of excess methoxynapthol in the surface coating of the structure of Example 1 permits heat-induced transfer of a portion thereof from the darkened image areas to an adjacent receptor sheet coated with the composition of the sub-coat to provide a color change. Fusible waxy or resinous materials may, under the influence of heat or solvent, be locally transferred from a surface of the irradiated imaged copysheet to an adjacent receptor sheet and there treated with colored dusts, oil-base inks, or other materials which selectively adhere to the tacky or otherwise receptive image areas. The initially heat-sensitive coating may be stripped from the paper-like support or backing onto an adhesive-coated sheet material to provide a mirror-image copy. Production of additional copies by spirit duplicating from an imaged copy-sheet in which the dye remains in colored spirit-soluble form exclusively in the image areas is likewise contemplated.

Compositions biased on certain diazo compounds are operable to a limited extent in the practice of this invention inasmuch as it has now been `found that the incorporation of small amounts of activatible silver-reducing colored organic dyes renders these compositions, and sheet materials appropriately prepared therewith, responsive not only to ultraviolet radiation but also to visible light of the higher wavelengths. Certain diazosulfonates, for example, are visibly heat-reactive with various azo coupler components. The reaction is inhibited by exposure to radiations of near-ultraviolet wavelength, but not by exposure to visible light such as green, yellow or red light. Incorporation of appropriate dyes makes possible the desensitization of the readily desensitizable diazosulfonate reactant by visible light. However the image colors and densities available from such compositions and sheet materials by heat alone do not provide the high contrast required in commercially acceptable copies.

Although the amount of dye used in these several desensitizable heat-sensitive copy-sheet systems may be varied `over wide ranges, it is preferred to employ minimal amounts so that the light may readily penetrate the dyed coating. It is also desirable, particularly in the structures of Examples 1 and 2, to minimize the concentration of dye so as to avoid undue color in the copy-sheet. However it is also necessary to include sufficient of the dye to provide a usefully rapid rate of desensitization under irradiation with visible light from commercially available sources.

The effect of varying concentrations of dye in terms of sheet color and of exposure time will now be indicated, by way of illustration and employing the system erythrosin/methoxynaphthol as described `under Example 3. The ratio of methoxynaphthol to polymeric binder is 0.3. Exposure is with a 500 watt tungsten projection lamp at 10,000 foot-candles. Exposure time is the time required to destroy the ability of the sheet to produce a visible reaction when heated in contact with the silvercontaining receptor sheet as described under Example 3. Concentration of dye is expressed in mols per rnol of the methoxynaphthol.

Concentration i Sheet Color Exposure Colorless 90 minutes. .001. do 7 minutes. .01. Light Pink.. seconds. .1.. Pink 16 seconds. 1 Red 30 seconds. (Saturated) Opaque Red seconds.

reactants, very small amounts of dye would not be expected to be suicient for any but a very minor and scarcely noticeable decrease in color-forming reactivity. Since the color-forming reaction is completely prevented at the illuminated areas, it appears that a further reaction must take place in which the reduced dye is again oxidized to its original state by reaction with mild oxidizing agents also present in the copy-sheet. ln some structures, oxidation may occur by a mechanism involving free oxygen from the surrounding atmosphere, or oxidizing agents such as peroxides which are known to be associated with organic ether materials. In others a mild reducing agent such as the triethanolamine of Example 4 may be provided to cause reduction of the activated dye, the reduced dye then being `re-oxidized by reaction with a mild oxidizing agent serving as one of the color-forming inter-reactants. The cycle is then repeated.

In any case, any regardless of the specific theoretical mechanism involved, the visibly inter-reactive, light-desensitizable systems employed in these novel copy-sheets comprise visibly chemically nter-reactant components for making a heat-sensitive copy-sheet useful in comunercial thermographic copying procedures, of which components one is readily desensitizable against such interreaction by irradiation in the near ultraviolet range of 3000-4200 angstroms; and, in intimate admixture with said one component, a colored activatible organic dye which is characterized as capable of causing reduction of silver ion under irradiation with light which is absorbable by said dye and is in the visible higher wavelength range.

In the appended explanatory drawing, FIGURE 1 represents a partial cross-section of a unitary heat-sensitive copy-sheet as more specifically described under Examples 1 and 2, and FIGURE 2 similarly represents the two laminae of a heat-sensitive copy-sheet product as described under Example 3. FIGURE 3 illustrates the product formed by adding to a structure such as that of FIGURE 1 a further surface layer of transferable imageforming material as described in connection with Example 8 and following Example 9. The modiied structure of Example 9 is illustrated in FIGURE 4.

What is claimed is as follows:

l. A heat-sensitive copy-sheet product capable of undergoing permanent visible change on being momentarily heated to a conversion temperature between about C. and about C. and comprising a heat-sensitive layer containing chemically inter-reactant components in physically distinct and chemically inter-reactive relationship for inter-reaction to form a visibly distinct reaction product on heating said layer to said conversion temperature, one of said inter-reactant components being readily desensitizable against said inter-reaction by exposure, in solution in an inert solvent at a concentration just sufcient to permit distinctly visible reaction with the other of said components in said solvent, to radiation in the near-ultraviolet range of approximately 3000 to 4200 angstroms wavelength as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes, and, uniformly intermixed with said one component, a colored activatible organic photoreducible dye characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolammoniurn nitrate, and said dye on exposure of said solution for thirty rninutes to visible light absorbable by said dye and at about 60,000 foot-candles intensity as obtained from a high intensity incandescent tungsten lilament lamp.

2. A heat-sensitive copy-sheet product capable of undergoing permanent visible change on being momentarily heated to a conversion temperature between about 90 C. and about 150 C. and comprising a heat-sensitive layer containing chemically inter-reactant components in physically distinct and chemically inter-reactive relationship for inter-reaction to form a visibly distinct reaction product on heating said layer to said conversion temperature, one of said inter-reactant components being readily desensitizable against said inter-reaction by exposure, in solution in an inert `solvent at a concentration just sufficient to permit distinctly visible reaction with the other of said components in said solvent, to radi-ation in the near-ultraviolet range of approximately 3000 to 4200 angstroms wavelength as obtained from a 13H-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes, and, unifonmly intermixed with said one component, a halogen-containing fluorescein photoreducible dye.

3. A heat-sensitive copy-sheet product capable of undergoing permanent visible change on being momentarily heated to a conversion temperature between about 90 C. and about l50 C. and comprising a heat-sensitive layer containing chemically inter-reactant components in physically distinct and chemically inter-reactive relationship for inter-reaction to form a visibly distinct reaction product on heating said layer to said conversion temperature, one of said inter-reactant components being readily desensitizable against said inter-reaction by exposure, in solution in an inert solvent at a concentration just sufficient to permit distinctly visible reaction with the other of said components in said solvent, to radiation in the near-ultraviolet range of approximately 3000 to 4200 angstroms wavelength as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes, and, uniformly intenmixed with said one component, a para-rosaniline photoreducible dye.

4. A heat-sensitive copy-sheet product capable of undergoing permanent visible change on being momentarily heated to a conversion temperature between about 90 C. and about 150 C. `and comprising a heat-sensitive layer containing chemically inter-reactant components in physically distinct and chemically inter-reactive relationship for inter-reaction to form a visibly distinct reaction product on heating said layer to said conversion temperature, one of said inter-reactant components comprising a substituted alpha-naphthol which is readily desensitizable against said inter-reaction by exposure, in solution in an inert solvent .at a concentration just sufcient to permit distinctly visible reaction with the other of said components in said solvent, to radiation in the near-ultraviolet range of approximately 3000 to 4200 angstroms wavelength as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes, and, uniformly intermixed with said alpha-naphfthol, a halogen-containing iluorescein photoreducible dye.

5. A heat-sensitive copy-sheet product capable of uuderfgoing permanent visible change on being momentarily heated to a conversion temperature between about 90 C. and about 150 C. and comprising a heat-sensitive layer containing chemically inter-reactant components in physically distinct and chemically inter-reactive relationship lfor inter-reaction to form a visibly distinct reaction iproduct on heating said layer to said conversion temperature, one of said inter-reactant components comprising a dithiooxamide which is readily desensitizable against said inter-reaction by exposure, in solution in an inert solvent `at a concentration just sufficient to permit distinctly visible reaction with the other of said components in said solvent, `to radiation in the near-ultraviolet range of approximately 3000 to 4200 angstrorns wavelength as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches vand for a time of 45 minutes, and, uniformly intermixed with said dithiooxamide, a halogen-containing uorescein photoreducible dye.

6. A unitary heat-sensitive copy-sheet capable of undergoing permanent visible change on being momentarily heated to a conversion temperature between about 90 C. and about 150 C. and comprising a thin paper-like backing and a visibly heat-sensitive layer comprising a hlm-forming binder, at least two chemically inter-reactant components in physically distinct and chemically inter- Vreactive relationship lfor rapidly inter-reacting at said conversion temperature to produce a visibly distinct reaction product nnd of which one of said components is readily desensitinable against said inter-reaction by exposure, in solution in an inert solvent at a concentration just sufiicient gto permit distinctly visible reaction with the other of said components in said solvent, to radiation in the near-ultraviolet range of approximately 3000 to 4200 angstroms wavelength as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes, `and a colored activatible organic photoreducible dye characterized by its ability to canse reduction of silver ion in a dilute solution of silver nitrate, triethanolammonium nitrate, and said dye on exposure of said solution for thirty yminutes to visible light of wavelength higher than 4500 angstroms and absorbable by said dye and at about 60,000 foot-candles intensity as obtained from a high intensity incandescent tungsten filament lamp.

7. A heat-sensitive copy-sheet product comprising, in face-to-face contact, (l) a thin paper-like backing sheet having a thin uniform face-coating including a rst reactant material and a colored activatible organic photoreducible dye in a hlm-forming binder, and (2) a thin paper-like backing sheet having a thin face coating including a second reactant material in a film-forming binder; said first and second reactant :materials being capable of rapidly inter-reacting at a conversion temperature between about C. and about 150 C. to produce a visibly distinct reaction product, said iirst reactant material being readily desensitizable against said inter-reaction by exposure, in solution in an inert solvent at a concentration just suicient to permit distinctly visible reaction with the other of said components in said solvent, to radiation in the near-ultraviolet range of approxi mately 3000 to 4200 angstroms wavelength as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes; and said dye being characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolarnm-onium nitrate, and said dye on exposure of said lsolution for thirty minutes to visible light in the wavelength range above 4200 angstroms and which is absorbable by said dye and at about 60,000 foot-candies intensity las obtained from a high intensity incandescent tungsten filament lamp.

8. A heat-sensitive copy-sheet product comprising, in tface-to-face contact, (l) a colored light-transmissive light-desensitizable intermediate film `material comprising a thin transparent exible lm backing having a thin face-coating including a film-forming binder, a substituted alpha-naphthol, and an activatible colored organic photoreducible dye, and (2) a receptor sheet portion comprising -a thin paper-like backing sheet having a thin face- Ycoating including a film-forming binder and a normally solid organic acid salt of a noble metal; said naphthol and said salt being inter-reactive to produce a colored reaction product on brie-f contact of said copy-sheet product with a :metal test bar at a conversion temperature within the range of about 90 t-o about 150 C.; said naphthol being volatilizable at said conversion temperature and being readily desensitizable against said inter-reaction by exposure, in solution in `an inert solvent at a concentration just sucient to permit distinctly visible reaction with said salt in said solvent, to radiation in the nearrultraviolet wavelength range of about 3000 to about 4200 Yangstrorns as obtained from a BH- high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes; and said dye being characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolammonium nitrate, and said dye on exposure of said solution `for thirty minutes to visible light in the range above 4200 angstroms and which is absorbable by said dye and at about 60,000 footcandles intensity as obtained from a high intensity incandescent tungsten filament lamp.

9. A heat-sensitive copy-sheet product comprising, in face-to-face contact, (1) `a thin transparent colorless flexible film backing having a thin uniform firmly bonded face-coating of components including 4-methoxy-l-naphthol and erythrosin, and (2) a thin paper-like backing sheet having a thin uniform rmly bonded face-coating including silver behenate.

10. For use in conjunction with a receptor sheet material comprising a thin paper-like backing sheet having a surface coating comprising a binder and a second reactant component, as a new product, a light-desensitizable intermediate sheet material comprising a thin paper-like backing sheet having a thin uniform surface coating comprising a binder, a first reactant component, and a colored activatible organic photoreducible dye characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolammonium nitrate, and said dye on exposure of said solution for thirty minutes to visible light absorbable by said dye and at about 60,000 foot-candles intensity as obtained from a high intensity `incandescent tungsten filament lamp and in the wavelength range above 4200 angstroms; said first and second reactant components being capable of rapidly chemically inter-reacting at a conversion temperature between about 90 C. and about 150 C. with production of a visibly distinct reaction product; said first reactant component being characterized as being readily desensitizable against said inter-reaction by exposure, in solution in an inert solvent at a concentration just sufficient to permit distinct ly visible reaction with said second reactant component in said solvent, to radiation in the approximate range of 3000 to 4200 angstroms wavelength as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes and being volatilizable at said conversion temperature.

11. For use in conjunction with a receptor sheet material comprising a thin paper-like backing sheet having a firmly bonded face-coating comprising a normally solid organic acid salt of a noble metal, as a new product, a light-desensitizable colored light-transmissive intermediate film Vmaterial comprising a thin transparent colorless flexible film backing having a thin uniform firmly bonded face-coating including a substituted alpha-naphthol interreactive with said salt to produce a colored reaction product on briey heating together said naphthol and said salt at a conversion temperature within the range of about 90 to about 150 C., and an activatible colored organic photoreducible dye; said naphthol being volatilizable at said conversion temperature and being readily desensitizable against said inter-reaction by exposure, in solution in an inert solvent at a concentration just sufficient to permit distinctly visible reaction with said salt in said solvent, to radiation in the near-ultraviolet wavelength range of about 3000 to about 4200 angstroms as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes; and said dye being characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolarnmonium nitrate, and said dye on exposure of said solution for thirty minutes to visible light in the range above 4200 angstroms and which is absorbable by said dye and at about 60,000 foot-candles intensity as obtained from a high intensity incandescent tungsten filament lamp.

12. A heat-sensitive copy-sheet product capable of becoming locally visibly altered and highly infra-red-absorptive on localized brief heating at a conversion temperature between about 90 C. and about 150 C., comprising a paper-like backing, a visibly heat-sensitive layer, and a surface layer comprising a heat-transferable imageforming component; said heat-sensitive layer comprising chemically inter-reactant components in physically distinct and chemically inter-reactive relationship for interreaction to form a visibly distinct and infra-red-absorptive reaction product on heating said layer to said conversion temperature, one of said inter-reactant components being readily desensitizable against said inter-reaction by exposure, in solution in an inert solvent at a concentration just sufficient to permit distinctly visible reaction with the otther of said components in said solvent, to radiation in the near-ultraviolet range of approximately 3000 to 4200 angstroms wavelength as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes, and, uniformly intermixed with said one component, a colored activatible organic photoreducible dye characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolammonium nitrate, and said dye on exposure of said solution for thirty minutes to visible light absorbable by said dye and at about60,000 footcandles intensity as obtained from a high intensity incandescent tungsten filament laimp.

13. A heat-sensitive copy-sheet product as defined in claim 6 in which the outer thickness of said heat-sensitive layer is visibly opaque and permanently transparentizable on heating at a temperature above about 100 C. and below degradation temperature.

14. In the method of making a light-desensitizable heatsensitive copy-sheet product having a heat-sensitive layer including chemically inter-reactant components in physically distinct and chemically inter-reactive relationship `for inter-reaction to form a visibly distinct reaction product on briefly heating said layer to a conversion temperature within the approximate range of to 150 C. and of which one of said components is readily desensitizable against said inter-reaction by exposure, in solution in an inert solvent at a concentration just sufficient to permit distinctly visible reaction with the other of said components in said solvent, to radiation in the near-ultraviolet wavelength range of approximately 3000 to 4200 angstroms as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes, the step of incorporating in said product and in intimate admixture with said one component a colored iactivatible organic photoreducible dye, said dye being characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolammoniurn nitrate, and said dye on exposure of said solution for thirty minutes to visible light absorbable by said dye and at about 60,000 foot-candles intensity as obtained from a high intensity incandescent tungsten filament lamp.

15. Method of copying comprising subjecting a heatsensitive copy-sheet as defined in claim 1 to visible light suicient to desensitize background areas against heatreaction and to heat sufiicient to produce in heat-sensitive image areas a chemical reaction resulting in a visible change.

16. The method of making a heat-stable copy of a graphic original having differentially radiation-absorptive image and background areas, comprising irradiating a heat-sensitive light-desensitizable copy-sheet product at least in areas corresponding to said background areas with visible light of wavelength at least 4200 angstroms to desensitize said background-corresponding areas, and heating said copy-sheet product at least in areas corresponding to said image areas and in no other heat-sensitive areas to cause a color change in said image-corresponding areas; said copy-sheet product being characterized as having a heat-sensitive ilayer containing chemically inter-reactant components in physically distinct and chemically inter-reactive relationship for inter-reaction to form a visibly distinct reaction product on heating said layer to said conversion temperature, one of said inter-reactant components being readily desensitizable against said interreaction by exposure, in solution in an inert solvent at a concentration just sufficient to permit distinctly visible reaction with the other of said components in said solvent, to radiation in the near-ultraviolet range of approximately 3000 to 4200 angstroms wavelength as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes, and, uniformly intermixed with said one component, a colored `activatible organic photoreducible dye characterized by 17 its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolannmonium nitrate, and said dye on exposure of said solution for thirty minutes to visible light absorbable by said dye and at about 60,- 000 foot-candles intensity as obtained from a high intensity incandescent tungsten lament lamp.

l?. The method of making a heat-stable copy of a graphic original having strongly infra-red-absorptive image areas which comprises irradiating said original with radiations rich in infra-red while in heat-conductive association with a heat-sensitive copy-sheet to provide an elevated-temperature pattern corresponding to said image areas and sufficient to produce a corresponding visible change in said copy-sheet, and then further irradiatiug said copy with visible light to desensitize the background areas; said copy-sheet being characterized as having a heat-sensitive layer containing chemically inter-reactant components in physically distinct and chemically interreactive relationship for inter-reaction to form a visibly distinct reaction product on heating said layer to said conversion temperature, one of said inter-reactant components being readily desensitizable against said interreaction by exposure, in solution in an inert solvent at a concentration just sutiicient to permit distinctly visible reaction with the other of said components is said solvent, to radiation in the near-ultraviolet range of approximately 3000 to 4200 angstroms wavelength as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes, and, uniformly intermixed with said one component, a colored activatible organic photoreducible dye characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolammonium nitrate, and said dye on exposure of said solution to visible light absorbable by said dye.

18. The method of making a copy of a graphic original having diiierentially light-absorptive image and background areas, comprising (l) placing over and in close Contact with said original a light-desensitizable colored light-transmissive intermediate lilm material comprising a thin transparent llexible iilm backing having a thin uniform firmly bonded face-coating including a first reactant and a colored activatible organic photoreducble dye, (2) exposing said original through said film material to visible light in the wavelength range above 4200 and of which at least a significant portion is absorbable by said dye and for a time and at an intensity suicient to cause total desensitization of said first reactant at areas corresponding to the least absorptive areas of said original and significantly less than total desensitization at areas corresponding to the -most absorptive areas of said original, (3) placing the thus exposed film material in face-to-face close contact with a receptor sheet comprising a thin paper-like backing sheet having a firmly bonded facecoating comprising a second reactant inter-reactive with said first reactant to produce a visibly distinct colored reaction product when said reactants are briefly heated together at a oonvension temperature within the range of about 90 C. to about 150 C., (4) heating to said conversion temperature to produce on said receptor sheet a visible reproduction of image areas of said original, and (5) separating said receptor sheet and said intermediate iilm; said rst reactant being further characterized as being readily desensitizable against said inter-reaction by exposure, in solution in an inert solvent at a concentration just sutlicient to permit distinctly visible reaction with said second reactant component in said solvent, to radiation in the near-ultraviolet Wavelength range of approximately 3000 to 4200 angstroms as obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for la time of 45 minutes; and said dye being characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, tricthanolammonium nitrate, and said dye on exposure of said solution for thirty minutes to visible light of Wavelength higher than 4200 angstroms and absorbable by said dye and Y18 at about 60,000 `foot-candles intensity as obtained from a high intensity incandescent tungsten hlamcnt lamp.

19. A unitary heat-sensitive copy-sheet capable of undergoing permanent visible change on being momentarily heated to a conversion temperature between about 90 C. and about 150 C. and comprising a thin transparent paper-like backing and a visibly heat-sensitive layer cornprising a film-forming binder, first and second chemically nter-reactant materials for rapid inter-reaction at said conversion temperature to produce a visibly distinct reaction product, and, `in intimate admixture with said first inter-reactaut material, a colored activatible organic photoreducible dye; and said copy-sheet including a visually non-transparent high contrast pigmented layer; said tirst material being readily desenstizable against said interr-eaction by exposure, in solution in an inert solvent at a concentration just sutlicient to penmit distinctly visible reaction with said second inter-reactant material in said solvent, to radiation in the near-ultraviolet wavelength range of approximately 3000 to 4200 angstroms as obtained from a BH- high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes, and being volatilizable at said conversion temperature; said second material being uniformly disposed between said backing and said opaque layer; and said dye being characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolammonium nitrate, and said dye on exposure of said solution for thirty minutes to visible light of Wavelength higher than 4500 angstroms and absorbable by said dye and at about 60,000 foot-candles intensity as obtained from -a high intensity incandescent tungsten filament lamp.

20. A unitary heat-sensitive copy-sheet capable of undergoing permanent visible change on being momentarily heated to a conversion temperature between about C. and about C. and comprising, in order, a thin transparent paper-like backing, a thin coating comprising a second reactant material, a thin non-transparent highly pigmented vapor-permeable binder layer, and a thin coating of components comprising, in intimate admixture, a vaporizable rst reactant material and a colored activatible organic photoreducible dye; said reactant materials being capable of rapid inter-reaction at said conversion temperature to produce a visibly distinct reaction product; said first reactant material being vaporizable at said conversion temperature and being readily desensitizable against said inter-reaction by exposure, in solution in an inert solvent at la concentration just sucient to permit distinctly visible reaction with said second reactant material in said solvent, to radiation in the near-ultraviolet range of approximate-1y 3000 to 4200 angstroms wavelength as obtained from a BHL-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes; and said dye being characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolammonium nitrate, and said dye on exposure of said solution for thirty minutes to visible light of wavelength higher than 4500 angstroms and absorbable by said dye and at about 60,000 foot-candles intensity as obtained from a high intensity incandescent tungsten lament lamp.

2l. A unitary heat-sensitive copy-sheet capable of undergoing permanent visible change on being momentarily heated toa conversion temperature between about 90 C. and about 150 C. and comprising, in order, a thin transparent paper-like backing, a thin coating comprising a second reactant material, and a thin non-transparent highly pigmented colored coating containing, in intimate admixture, a first reactant material and a colored activatble organic photoreducible dye; said tirst and second reactant materials being capable of rapid inter-reaction at said conversion temperature to produce a visibly distinct reaction product; said rst reactant material being vaporizable at said conversion temperature and being readily desensitizable against said inter-reaction by exposure, in solution in an inert solvent at a concentration just sufi'icient to permit distinctly visible reaction with said second reactant material in said solvent, to radiation in the nearultraviolet range of approximately 3000 to 4200 angstroms wavelength as `obtained from a BH-6 high pressure mercury arc lamp at a distance of 6 inches and for a time of 45 minutes; and said dye being characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolammonium nitrate, and said dye on exposure of said solution for thirty minutes to visible light of wavelength higher than 4500 angstroms and absorbable by said dye and at about 60,000 footcandles intensity as obtained from a high intensity incandescent tungsten lament lamp.

22. As a new product suitable for use in conjunction with a receptor sheet material having a coating of silver bchenate on a paper-like backing sheet, a light desensitizable colored light-transmissive intermediate lm material comprising a thin transparent colorless iiexible lm backing having a thin uniform firmly bonded face-coating of components including 4-methoxy-1-naphthol and erythrosm.

23. A heat-sensitive copy-sheet product comprising, in face-to-face contact, (l) a thin transparent colorless exible film backing having a thin uniform firmly bonded face-coating of components including 4methoxy1 naphthol and erythrosin, and (2) a thin paper-like backing sheet having a thin uniform firmly bonded face-coating including a normally solid organic acid salt of a noble metal.

24. A heat-sensitive copy-sheet product comprising, in face-to-face contact, (1) a thin transparent colorless iiexible film backing having a thin uniform tirmly bonded face-coating of components including a substituted naphthol and a halogen-containing uoresoein dye, and

(2) a thin paper-like backing sheet having a thin uniform firmly bonded face-coating including a normally solid organic acid salt of a noble metal; said naphthol and said metal salt being interreactive to produce a colored reaction product on brief contact of said copy-sheet product with a metal test bar at a temperature within about 90-150 C.; said naphthol being volatilizable at said temperature and being readily desensitizable against said inter-reaction by exposure to near-ultraviolet radiation; said dye being characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolammonium nitrate, and said dye on exposure visible light in the range above 4200 angstroms and which is absorbable by said dye.

25. A heat-sensitive copy-sheet product having a lightdesensitizable visibly heat-sensitive layer including a nickel salt, a dithiooxamide which is visibly inter-reactive with said nickel salt on momentary heating of said copysheet to about 90-150 C. and which is desensitizable against such inter-reaciton by exposure to near-ultraviolet radiation, and a halogen-containing uorescein dye characterized by its ability to cause reduction of silver ion in a dilute solution of silver nitrate, triethanolammonium nitrate, and said dye on exposure t-o visible light in the range above 4200 angstroms and which is absorbable by said dye.

References Cited in the file of this patent UNITED STATES PATENTS 2,910,377 Owen Oct. 27, 1959 2,967,784 Newman et al. Jan. 10, 1961 2,967,785 Allen et al. Jan. 10, 1961 

18. THE METHOD OF MAKING A COPY OF A GRAPHIC ORGANICAL HAVING DIFFERENTIALLY LIGHT-ABSORPTIVE IMAGE AND BACKGROUND AREAS, COMPRISING (1) PLACING OVER AND IN CLOSE CONTACT WITH SAID ORGINAL A LIGHT-DENSENSITIZABLE COLORED LIGHT-TRANSMISSIVE INTERMEDIATE FILM MATERIAL COMPRISING A THIN TRANSPARENT FLEXIBLE FILM BACKING HAVING A THIN UNIFORM FIRMLY BONDED FACE-COATING INCLUDING A FIRST REACTANT AND A COLORED ACTIVATIBLE ORGANIC PHOTOREDUCIBLE DYE, (2) EXPOSING SAID ORIGINAL THROUGH SAID FILM MATERIAL TO VISIBLE LIGHT IN THE WAVELENGTH RANGE ABOVE 4200 AND OF WHICH AT LEAST A SIGNIFICANT PORTION IS ABSORBABLE BY SAID DYE AND FOR A TIME AND AT AN INTENSITY SUFFICIENT TO CAUSE TOTAL DENSENSITIZATION OF SAID FIRST REACTANT AT AREAS CORRESPONDING TO THE LEAST ABSORPTIVE AREAS OF SAID ORGINAL AND SIGNIFICANTLY LESS THAN TOTAL DESENSITIZATION AT AREAS CORRESPONDING TO THE MOST ABSORPTIVE AREA OF SAID ORIGINAL, (3) PLACING THE THUS EXPOSED FILM MATERIAL IN FACE-TO-FACE CLOSE CONTACT WITH A RECEPTOR SHEET COMPRISING A THIN PAPER-LIKE BACKING SHEET HAVING A FIRMLY BONDED FACECOATING COMPRISING A SECOND REACTANT INTER-REACTIVE WITH SAID FIRST REACTANT TO PRODUCE A VISIBLY DISTINCT COLORED REACTANT PRODUCT WHEN SAID REACTANTS ARE BRIEFLY HEATED TOGETHER AT A CONVERSION TEMPERATURE WITHIN THE RANGE OF ABOUT 90*C. TO ABOUT 150*C., (4) HEATING TO SAID CONVERSION TEMPERATURE TO PRODUCE ON SAID RECEPTOR SHEET A VISIBLE REPRODUCTION OF IMAGE AREAS OF SAID ORIGINAL, AND (5) SEPARATING SAID RECEPTOR SHEET AND SAID INTERMEDIATE FILM; SAID FIRST REACTANT BEING FURTHER CHARACTERIZED AS BEING READILY DESENSITIZABLE AGAINST SAID INTER-REACTION BY EXPOSURE, IN SOLUTION IN AN INERT SOLVENT AT A CONCENTRATION JUST SUFFICIENT TO PERMIT DISTINCTLY VISIBLE REACTION WITH SAID SECOND REACTANT COMPONENT IN SAID SOLVENT, TO RADIATION IN THE NEAR-ULTRAVIOLET WAVELENGTH RANGE OF APPROXIMATELY 3000 TO 4200 ANGSTROMS AS OBTAINED FROM A BH-6 HIGHT PRESSURE MERCURY ARC LAMP AT A DISTANCE OF 6 INCHES AND FOR A TIME OF 45 MINUTES; AND SAID DYE BEING CHARACTERIZED BY ITS ABILITY TO CAUSE REDUCTION OF SILVER ION IN A DILUTE SOLUTION OF SILVER NITRATE, TRIETHANOLAMMONIUM NITRATE, AND SAID DYE ON EXPOSURE OF SAID SOLUTION FOR THIRTY MINUTES TO VISIBLE LIGHT OF WAVELENGTH HIGHER THAN 42000 ANGSTROMS AND ABSORBABLE BY SAID DYE AND AT ABOUT 60,000 FOOT-CANDLES INTENSITY AS OBTAINED FROM A HIGH INTENSITY INCANDESCENT TUNGSTEN FILAMENT LAMP. 